The field of the disclosure relates generally to protecting an electric motor drive controller from damage, and more specifically, to protecting an electric motor drive controller and connected electronics from transient and/or ringing voltages.
Electric motors are used in numerous varieties and applications worldwide. For example, electric motors are included within heating, ventilation, and air conditioning (HVAC) applications. A typical HVAC application includes a thermostat, a furnace or a fan coil, a system controller, a motor controller, and at least one electric motor. Since the motor controller is a component within a larger system, the motor controller may be subject to transient voltages caused by, for example, power system switching and/or lightning strikes. Switching transients may be caused by power system switching, load changes in power distribution systems, and/or short circuit fault conditions. Furthermore, the motor controller may be subject to transient voltages caused by events external to the HVAC application, for example, power surges. Power surges may be caused by different external forces, most typically, from lightning strikes. Lightning strike transients may result from a direct strike or induced voltages and currents due to an indirect lightning strike.
Known motor controllers include large capacitance electrolytic capacitors (i.e., above about 10 microfarads per kilowatt (μF/kW)) on a rectified direct current (DC) link that provide a secondary function of preventing large voltage surges or transients (i.e., above about 500 volts (V)) that may occur on an AC line input connection due to switching or lightning, creating an overvoltage failure mode on the DC link.
If instead of large electrolytic capacitors, a low capacitance (i.e., between about 0.1 μF/kW and about 10 μF/kW) film capacitor is used across the DC link, the motor controller may become susceptible to overvoltage failure modes. To prevent overvoltage failure, a voltage clamping circuit may be used. However, typical clamping circuits may not provide the same level of protection as the known large capacitance electrolytic capacitors, and accordingly, may not sufficiently protect the motor controller from a transient voltage.